1. Field of the Invention
The present invention relates to an ethylene type ternary copolymer useful as a modifier for resins such as a polypropylene and also to a propylene type resin composition containing this ethylene type ternary copolymer.
2. Description of the Related Art
Conventionally, Measures taken to compound elastomers, such as an ethylene/propylene copolymer and ethylene/butene copolymer, as a modifier in a polypropylene resin with the intention of improving the tensile elongation at break and impact resistance of a polypropylene resin have been well known.
However, if an elastomer is compounded in a polypropylene resin, the rigidity of the resin is dropped and there is therefore limitation to the amount of the elastomer to be compounded. Also, there is the case where it is demanded of, for instance, resin molded articles such as a polypropylene resin molded article to have not only impact resistance at normal temperature but also impact resistance at low temperatures. Therefore, such a modifier as to retain the balance between rigidity and impact resistance at a high level is desired.
On the other hand, it is demanded of resin molded articles such as those mentioned above not to be broken in practical use. Therefore, it is demanded of these resin molded articles to have high tensile strength at break and impact strength while maintaining high rigidity. Specifically, it has been desired to develop a resin modifier which also has a high level of balance between rigidity and tensile elongation at break.
A trial is made to obtain a composition having a good quality balance between rigidity and impact resistance by compounding an ethylene/propylene copolymer or an ethylene/butene copolymer having specific properties in a polypropylene polymer. However, this composition is inferior in the balance between rigidity and impact resistance. If an ethylene/α-olefin copolymer obtained by copolymerizing a higher α-olefin having many carbon atoms, namely a higher α-olefin having 6 or more carbon atoms is compounded, the tensile elongation at break is improved. However, these α-olefins are expensive and it is therefore necessary to limit the amount of these α-olefins to the minimum (see, for example, Publication of JP-A No. 6-192500 or Publication of JP-A No. 8-302096). Also, a ternary copolymer of ethylene/propylene or 1-butene/α-olefin having 6 to 20 carbon atoms is also disclosed. However, this copolymer does not aim at the use of a polypropylene polymer modifier (Publication of JP-A No. 9-87330).